Map showing the two major towns in the hands of rebels where intense fighting has been reported

An AFP photographer touring the two oil states of Unity and Upper Nile went to villages around Bentiu, the Unity state capital, which government forces wrested back from rebels on Friday, and saw corpses in the streets and the thatched roofs of torched mud huts still smouldering.

Malakal, the main town in the biggest oil-producing state Upper Nile, has been calm for several days but most residents remain too scared to return to their looted or torched homes, the photographer said.

Meanwhile the Satellite Sentinel Project, co-founded by Hollywood star George Clooney, released images detailing destruction to homes and markets in two towns, Mayom in oil-rich Unity and Bor, the Jonglei state capital, which government forces are trying to take back from rebels for the second time in a month.

"Evidence of atrocities against civilians should be collected and used for future prosecution for war crimes. There will be no peace if massive human rights abuses can be committed with no accountability," Clooney said in a statement.

A soldier from the South Sudan Liberation Army (SPLA) winces as a doctor treats a bullet wound at a health centre in the village of Minkamen in Awerial county, South Sudan on January 11, 2014

Fighting continued Sunday around the flashpoint town of Bor, rebel military spokesman General Lul Ruai Koang told AFP.

"We are still holding our positions, but the government forces are shelling them," he said, adding he did not know if close combat was also taking place.

Mediation efforts rise a notch

Mediations efforts rose a notch meanwhile.

US envoy Donald Booth told journalists he and other mediators had spent over three hours with Machar in an undisclosed location in South Sudan "trying to move him toward agreeing to sign a cessation of hostilities agreement".

Booth confirmed that a major sticking point remains the 11 Machar sympathisers arrested by forces loyal to President Salva Kiir shortly after the fighting began.

Machar's side has insisted the detainees should be released, while Kiir is equally adamant they should face justice.

Riek Machar, then Vice President of South Sudan, pictured at the UN headquarters in New York on July 13, 2011

"We continue to put pressure on both sides -- on both sides to sign the agreement and also on the government to agree to the release of the 11 ... who remain detained in Juba," Booth said.

The meeting with Machar, a former vice president and seasoned rebel fighter, and the trip to see Kiir come as talks in the Ethiopian capital Addis Ababa appear to be running out of steam. Mediators for the East African regional bloc IGAD have been trying to incorporate the proposals of both sides into a draft ceasefire document.

Fighting erupted in South Sudan on December 15. Kiir accused Machar of attempting a coup. Machar in turn accused Kiir of using the coup accusation as an excuse to carry out a purge.

What began as clashes within army units spread rapidly with government troops fighting huge battles against breakaway soldiers and ethnic militiamen loosely allied to Machar.

The conflict sparked a sharp upsurge in ethnic violence between members of Kiir's majority Dinka tribe and Machar's Nuer community.

UN chief Ban Ki-moon warned that evidence of widespread atrocities committed during the month-long conflict would be investigated, and the perpetrators "held accountable."a

The fighting has forced nearly 400,000 people to flee their homes and caused "very substantially in excess" of 1,000 dead, according to the United Nations.

International Crisis Group, an independent think-tank, estimated as many as 10,000 people have been killed in the month of fighting in the country, which won independence from Khartoum only in 2011.

Of those forced to flee, some 350,000 are internally displaced and the remainder have fled into neighbouring countries.

The UN's refugee agency said Sunday that around 10,000 people have fled north into Sudan, making it the second-largest recipient of refugees after Uganda.

Thanks Chiki for this article. I don't understand why they even waste time threatening them with prosecution of "war crimes," nothing ever gets done. How long have has the ICC had a warrant out for Omar al Bashir, it's a joke. I'm very disappointed with President Obama, he has done so little. Same as with other governments, it is an abomination against the Sudanese people.

Every day that is wasted more and more people are being slaughtered. They need to stop the talking and do something. I'm feeling exasperated imagine how the Sudanese people are feeling. They are amazing going on day after day just waiting for help and not giving up. God Bless them. XXX

I agree, Obama's foreign policy hasn't been his strong point. And of course, it can apply to UE as well. Seems sooooo difficult bringing him to ICC. I know exactly how you feel, but it isn't waste time, as you know. Yes, for sudanese people every day counts, but I'm sure he finally will fall, and then every evidence will be importante. We must keep faith in it. But you are right, every day is harder.